A communication system typically involves transmitting a modulated representation of a communication signal from a transmitter to a receiver over a communication channel. The communication channel may include a microwave radio link, a satellite channel, a fiber optic cable, or a copper cable to provide some examples. A communication channel contains a propagation medium that a transmitted communication signal passes through before reception by the receiver.
The propagation medium of the communication channel introduces interference and/or distortion into the transmitted communication signal causing a received communication signal to differ from the transmitted communication signal. Noise, signal strength variations known as fading, phase shift variations, multiple path delays known as multi-path propagation or echoes, to provide some examples, may introduce distortion into the transmitted communication signal. For example, transmission over a multiplicity of paths of different and variable lengths, or rapidly varying delays in the propagation medium from the transmitter to the receiver, may cause a change in the amplitude and/or phase of the transmitted communication signal. The communication channel may also introduce interference resulting from undesirable signals and/or noise into the transmitted communication signal causing the received communication signal to differ from the transmitted communication signal. The transmitter and/or the receiver may introduce interference and/or distortion into the transmitted communication signal causing the received communication signal to differ from the transmitted communication signal.
Communication systems may use an adjustable filter in the form of an adaptive equalizer to reduce the effect of the interference and/or the distortion attributable to the communication channel, the transmitter, and/or the receiver. To compensate for the interference and/or the distortion attributable to the communication channel, the transmitter, and/or the receiver, the adaptive equalizer adaptively adjusts an impulse response by updating equalization coefficients through, for example, a least-squares algorithm, such as the widely known Least Mean Squared (LMS), Recursive Least Squares (RLS), Minimum Mean Squared Error (MMSE) algorithms or any suitable equivalent algorithm that yields a least-squares result such as a dithering algorithm as disclosed in U.S. patent application Ser. No. 10/879,673, entitled “System and Method for Adjusting Multiple Control Loops Using Common Criteria,” filed on Jun. 29, 2004, now U.S. Pat. No. 7,961,823, which is incorporated by reference in its entirety. In other words, the least-squares algorithm or the suitable equivalent algorithm may train the adaptive equalizer to compensate for the interference and/or the distortion uncorrelated with the transmitted communication signal. However, a conventional adaptive equalizer uses a scheme tantamount of time-averaging to determine correlation between the interference and/or the distortion and the transmitted communication signal. Those skilled in the relevant art(s) will recognize that the concepts disclosed within may be applicable to, but are not limited to, adaptive equalizers trained using a least-squares algorithm, or equivalent or near-equivalent, for coefficient adaptation, including block processing methods, recursive methods, slightly modified methods such as tap draining or inclusion of biasing signals or methods to provide stability, dithering methods and gradient methods, and/or multiple optimizations taking place in parallel with the adaptive equalizer to provide some examples.
Commonly, the interference and/or the distortion introduced by the communication channel may include one or more time-varying noise and/or interference conditions. As a result, the conventional adaptive equalizer may not properly determine the correlation between the interference and/or the distortion currently present and the transmitted communication signal. As a result of determining the correlation using scheme tantamount of time-averaging, the least-squares algorithm or the suitable equivalent may inadequately train the conventional adaptive equalizer to compensate for the interference and/or the distortion resulting from the transmitter, the communication channel, and/or the receiver impressed onto the transmitted communication signal in the presence of the one or more time-varying noise and/or interference conditions.
Therefore, what is needed is an adaptive equalizer that is capable of compensating for the interference and/or the distortion resulting from the communication channel, the transmitter, and/or the receiver impressed onto the transmitted communication signal in the presence of the one or more time-varying noise and/or interference conditions.
The present invention will now be described with reference to the accompanying drawings. In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. The drawing in which an element first appears is indicated by the leftmost digit(s) in the reference number.